Human blood is composed of cellular components (RBCs, WBCs and platelets) and plasma. Plasma comprises biomarkers or analytes which contain several health related important information of human beings. Therefore, plasma separation from human blood is very useful for diagnosis of diseases in human beings. Microfluidic devices are used for separating plasma from human blood.
Microfluidic devices are broadly classified into two main groups or categories, namely active microdevices and passive microdevices. Active microdevices require external forces for their operation, whereas passive microdevices do not require external forces for their operation. Passive microdevices are subclassified into several subcategories. Hydrodynamic microdevices are a subclass of passive microdevices which make use of bio-physical effects, microchannel geometry and flow rates for their operation. Besides having the advantage of not requiring external force for their operation, dynamic passive microdevices have further advantages such as ease of fabrication, simplicity of design and potential to provide clog-free, continuous operation.
Kerhoas et al teach a microdevice comprising a main channel having width 100 μm and depth 20 μm and 8 plasma channels placed at an angle of 45° to the main channel. Two microdevices of plasma channel widths of 20 μm and 10 μm and depth 20 μm are reported. In the case of the microdevice having plasma channel width of 10 μm, a plasma separation efficiency of 99% is reported with whole human blood (haematocrit content 45%) at a flow rate of 2 ml/hr. Plasma yield is reported to be 5% [Kersaudy-Kerhoas, M., Kavanagh, D. M., Dhariwal, R. S., Campbell, C. J., & Desmulliez, M. P. (2010). Validation of a blood plasma separation system by biomarker detection. Lab on a Chip, 10(12), 1587-1595].
Blattert et al teach a microdevice comprising a main channel having bend angle of 90° and bend radius of 500 μm. The width of the main channel is varied between 20 μm to 100 μm. A microdevice of inlet width 42 μm, outlet width 97 μm, plasma channel width 28 μm and depth 116 μm and flow rate ratio of 0.03 (the ratio of the flow rate in the plasma channel to the flow rate in the blood outlet) is reported to give a plasma separation efficiency of 58% and 90% with blood hematocrit content of 45% and 5%, respectively at a feed velocity of 2 m/s. Plasma yield is reported to be 5-10% [Blattert, C., Jurischka, R., Schoth, A., Kerth, P., & Menz, W. (2004, Jan.). Separation of blood in microchannel bends. In Micromachining and Microfabrication (pp. 17-25). International Society for Optics and Photonics].
Tripathi et al teach a T-shaped microdevice comprising a main channel of width 400 μm and depth 50 μm and a plasma channel of width of 100 μm and depth of 50 μm. At a flow rate of 0.15 ml/min, flow rate ratio of 54:1 and haematocrit content of 45%, a plasma separation efficiency of 45% and a plasma yield of 1.91% are reported. At the same flow rate and flow ratio and haematocrit content of 2%, a plasma separation efficiency of 99% is reported [Tripathi, S., Prabhakar, A., Kumar, N., Singh, S. G., & Agrawal, A. (2013). Blood plasma separation in elevated dimension T-shaped microchannel. Biomedical microdevices, 15(3), 415-425].
Prabhakar et al teach a hybrid microdevice comprising a microchannel having inlet width 200 μm and depth 60 μm and a plasma channel width 100 μm and depth 60 μm. A plasma separation efficiency of 100% is reported using diluted blood of haematocrit content 15% and a plasma separation efficiency of 80% is reported with whole human blood of haematocrit content 45% at a flow rate of 0.4 ml/min. Plasma yield is reported to be 3% with whole human blood. [Prabhakar, A., Kumar, Y.V.B.V., Tripathi, S., & Agrawal, A. (2014). A novel, compact and efficient microchannel arrangement with multiple hydrodynamic effects for blood plasma separation. Microfluidics and Nanofluidics, 18(5-6), 995-1006].
Although numerous microdevices for separating plasma from human blood are known and reported, they are mostly for separating plasma from diluted blood. This involves the step of dilution of the blood prior to plasma separation. The plasma separation efficiency of the microdevices in general is poor and decreases as the hematocrit content in the blood increases. Besides, the microdevices comprise microchannels having very small dimensions in the range of microns. As a result, they are difficult and expensive to fabricate and are at risk of clogging leading to failure and discontinuous operation of the microdevices. During dilution, there are chances for the biomarkers to get lost. When a biosensor is integrated with a microdevice using diluted blood, the sensitivity of the microsensor is reduced due to the diluted blood. Accuracy of diagnosis using biomarkers depends on the concentration of biomarkers in the plasma. The higher the concentration of biomarkers, the better the accuracy of diagnosis. Therefore, use of whole blood (with hematocrit of about 42% or more) for plasma separation is advantageous to get high concentrations of biomarkers in the plasma. Use of whole blood is also advantageous in that it eliminates the step of blood dilution. Microdevices having high plasma separation efficiency are advantageous and desirable.
There is thus scope and need for microdevices for separation of plasma from human blood, which are very efficient and effective in plasma separation from human blood having a wide range of hematocrit (Hct) content, especially whole blood and which have other advantages and benefits such as ease of fabrication, simplicity of design, clog free and continuous operation and capability of being easily integrated with biosensors.